Where does “fastmine” come from?

fastmine (English) comes from English fast, from Middle English fast, from Old English fæste, from Old English -e, from Old English -en, from Old Norse -inn, from Proto-Norse -īna-, from Proto-Germanic -īnaz — adjectival suffix.

Ancestry of “fastmine”, step by step

fastmine traces back through two separate lines of ancestry.

via English fast

StepLanguageWordMeaning
1EnglishfastFirmly or securely fixed in place; stable; Firm...
2Middle Englishfastfast quickly
3Old Englishfæstefirmly, fastly, tightly
4Old English-eforming adverbs from adjectives; -ly
5Old English-enmæġþ + API → mæġden; cocc + API → cycen, cicen;...
6Old Norse-innUsed to create adjectives from nouns, meaning...
7Proto-Norse-īna-
8Proto-Germanic-īnaz-en
9Proto-Indo-European-iHnosCreates adjectives of materials
10Proto-Indo-European-no-adjectival suffix

via English Mine

StepLanguageWordMeaning
1EnglishMineAlternative letter-case form of mine "often used...
2Frenchminemine; pencil lead; piledriver, scorcher
3Bretonminface of an animal; beak, muzzle
4Italianminamine, land mine; lead in pencils; mine which...
5LatinminaA Greek weight equal to 100 drachmas; A Greek...
6Gaulishmēnāore, mine
7Proto-Celtic*meinisore, metal
8Proto-Indo-Europeanmēy(H)nis
9Proto-Indo-European(s)mēy(H)-to cut, hew
Every word from Proto-Indo-European -no-Every word from Proto-Germanic -īnazEvery word from Old English -en